1. Field of the Invention
The present invention relates to a turret punch press machine having a pair of turrets on which plural dies are mounted, and more particularly, to a turret punch press machine capable of preventing the paired turrets from being shifted from each other when their frames are deformed.
2. Prior Art
Various kinds of the turret punch press machines have been proposed these days and they can be classified into those of C-shaped frame type and those of gate-shaped frame type.
The conventional turret punch press machine of the C-shaped frame type is arranged as shown in FIG. 1. Numeral 10a represents a frame, which comprises a base frame portion 12a, a column portion 14a and an upper frame portion 16a and which is shaped in the form of letter "C". A hammer 18 is arranged at the front end of the upper frame portion 16a and driven by a hammer driving mechanism 20. This machine is also provided with a pair of turrets 22 and 24. The upper turret 22 is freely rotatably attached to the upper frame portion 16a by means of a shaft 34, whereas the lower turret 24 is rotatably attached to the base (or lower) frame portion 12a by means of a shaft 36. These turrets have plural dies at the circumferential rim portion thereof. Each of these dies consists of upper and lower halves 26 and 28. A work 30 is inserted between the upper and lower halves of dies on the turrets by means of a work movement positioning mechanism 32. The turrets are rotated, the halves of a selected die are positioned under the hammer, and then the hammer is pushed down and the upper half 26 is pressed, thereby punch-processing the work 30.
The pressing force applied on the hammer 18 amounts to 20-50 tons. The upper frame portion 16a is thus deformed, as shown in FIG. 1 (where the deformation is exaggerated), by the repulsive force of the hammer 18 which is being operated. As the result, the upper and lower turrets 22 and 24 are shifted from each other, and the upper and lower halves 26 and 28 come to have an undesired positional relationship. The work 30, thus, comes to have burrs and other deformation at its punched portion, thereby reducing processing accuracy and shortening the lifetime of the dies. The deformation of the frame is caused in the horizontal direction as well as in the vertical direction. It is also caused by heat created by the hammer driving mechanism and the aging change of the frame, as well as the repulsive force of the hammer. This frame deformation causes the positional accuracy of the upper and lower halves to become wrong, thereby decreasing the processing accuracy and the lifetime of the dies.
The conventional turret punch press machine of the gate-shaped type is schematically shown in FIG. 2. It is provided with a frame 10b comprising a lower frame portion 12b, a pair of column portions 14b and an upper frame portion 16b, and it has the same arrangement except for the frame as that in the press machine shown in FIG. 1. Even in the case of this press machine of the gate-shaped frame type, the frame is deformed, as shown in FIG. 2 (where the deformation is also exaggerated), by the repulsive force of the hammer and the like. Consequently, the upper and lower halves come out of order in their positional relationship. The turret punch press machine of this type is disclosed in U.S. Pat. No. 4,412,469 to Hirata et al. This device is fundamentally the same in arrangement as that shown in FIG. 2 and the positional relationship of the die halves is also made wrong because of the frame deformation.
The above-mentioned disadvantages caused by the frame deformation are more prominent as the machine becomes larger in size and the processing accuracy required becomes higher on a thin work piece. In order to compensate the aging deformation of the frame caused by various causes, the conventional large-sized and high accuracy turret punch press machines make it necessary to periodically adjust positions of the turrets and other parts.